In recent years, various services are offered through a computer network, and Web service techniques are being used. The Web service is a mechanism to dynamically exchange data between computers using a variety of communication protocols typified by HTTP without human intervention. In the Web service, a SOAP message flows between a client and a server based on the communication protocol, and various computer devices, built-in devices, and the like can receive information.
The use of the Web service allows exchanging SOAP messages containing not only texts but also large data such as an image. When a client transmits a large SOAP message to a server that provides a service for accepting a SOAP message, it takes time to end the transmission of the SOAP message. Hence, the need arises for a control mechanism of, when the client wants the server to receive an urgent SOAP message first during transmission of a large SOAP message, preferentially transmitting the urgent SOAP message.
As a technique of controlling priority between the client and the server, priority is controlled at the IP packet level by assigning a priority level to each IP packet flowing through the network. This priority control technique is implemented by interposing a relay device between the client and the server to interpret the priority level of an IP packet and transmit a packet having a high priority level (see, for example, patent literature 1).